The present disclosure relates to optical waveguides, and more specifically to optical waveguides in photonic integrated circuits.
A common wafer used in manufacturing integrated devices is an SOI (Silicon On Insulator) wafer. The SOI wafer has a silicon layer (SOI layer) formed on a buried oxide (insulator) film, which is commonly referred to as the BOX layer. The SOI wafer has small parasitic capacitance and high radiation resistance. The upper SOI layer, where devices are formed, is electrically and optically separated from the lower portion of the substrate by the BOX. Therefore, the SOI wafer produces high-speed and low-power consumption operation, prevents soft errors, and is regarded as a high-performance semiconductor device.
In many cases, the SOI wafers are produced by bonding methods, where a silicon oxide film is formed on the front surface of a silicon single crystal wafer, and then another silicon single crystal wafer is bonded to the oxide film on the first wafer. The bonding strength can be increased by performing bonding heat treatment. Also, one of the wafers (e.g., the SOI layer) can be thinned by mirror polishing or ion implantation to achieve desired performance and size considerations. Photonic integrated circuits (PIC) often form optical waveguides and other optical structures using the SOI layer.